ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
107 
room. 1 have no experience with the arc light in the micro-lantern, 
and therefore my remarks do not apply to this. — Tuos. Fletcher.” 
(2) Eye-pieces and Objectives. 
Zeiss’s New Microscope Objective.* — Count F. Castracane referred 
to the now Zeiss’s objective of 1/10 in. focal length and numerical 
aperture 1 • 63, and the beautiful photomicrograms of Ampliipleura 
pellucida taken by Dr. Van Heurck to test its value. In these the 
square structure of the minutest grain is clearly visible. The magni- 
fication employed amounted, according to Van Heurck, to 2000 diameters, 
and consequently the longitudinal divisions would amount to 5000 to 
the mm., thus exceeding considerably the limit of visibility deter- 
mined by Helmholtz’s theory. As no mention was made of such a result 
by Prof. Abbe when he demonstrated the utility of an illuminating cone 
of wide aperture in connection with the new Zeiss objective, it seems 
possible that Van Heurck has made a mistake in assigning the magnifica- 
tion, especially when it is considered how little reliance can be placed 
upon the magnifications given by the makers of Microscopes. 
(3) Illuminating- and other Apparatus. 
New Hot Stage-t— M. Drosten describes a new hot stage which 
will be found very serviceable in microscopy. It consists (fig. 6) 
of a shallow box made of 
glass plates soldered to- 
gether by an enamel which 
is not affected by heat or 
liquids. In one of the side 
walls of the box a thermo- 
meter and two glass tubes 
a and b are fixed. The 
beating of the stage is 
effected by a stream of warm water, which enters by the tube a and 
passes out by tube b. By regulating the flow of water in b by means of 
a clamp a very constant temperature, only varying by half a degree, can 
be obtained. The stage, being entirely of glass, can be used with all 
objectives up to the highest magnification. 
Glass Slide-boxes.:}: — M. Drosten describes slide-boxes constructed 
of glass plates united by an enamel which is not dissolved by alcohol 
* Atti Acc. Pontif. de' Nuovi Lincei, xliii. (1890) pp. 215-6. 
t Bull. Soc. Belg. Micr., xviii. (1891) pp. 5-7. t Ibid. 
